Payback — Sam Stewart

Someone's poisoning an artificial sweetener and people across the country are dying at random. It's part of a plot to get back at Bob Mitchell, the company's president, a decorated war hero trailed by a past, whose secrets, if exposed, could blow up his future. The police have nothing, the body count's nine, and Mitchell's got four days to track down the killer or the man kills and again explodes Mitchell's life.
 
From Hollywood, where death is just the hook for a movie, to Switzerland, where sex is just a numbered account, Mitchell's hunt leads him to a shattering discovery, a long lost lover, and a battle as ferocious as any in the war.